Chemistry · Ch 10 — Biomolecules
Classification of Vitamins
Classification of Vitamins
The Basis of Classification
Vitamins are sorted into two broad groups purely on the basis of one physical property: whether they dissolve in water or in fat. This single criterion — solubility — turns out to have far-reaching consequences for how each group behaves inside the body, how it needs to be supplied through diet, and even how dangerous an excess of it can be.
Fat-Soluble Vitamins
The first group consists of vitamins that dissolve readily in fats and oils but not in water. Vitamins A, D, E, and K all fall into this category. Because they are fat-loving (lipophilic) rather than water-loving, the body is able to store them away in fatty tissue — specifically in the liver and in adipose (fat-storing) tissue. This storage capacity means the body can build up a reserve of these vitamins over time rather than needing a constant fresh supply.
Water-Soluble Vitamins
The second group is soluble in water rather than in fat, and it comprises the B-group vitamins together with vitamin C. Because these compounds mix freely with the aqueous fluids of the body, they cannot be tucked away in fatty depots the way the fat-soluble vitamins can — the kidneys readily filter them out, and they are excreted in the urine once the body's immediate needs are met. As a direct result, water-soluble vitamins cannot be stored in the body in any meaningful amount (with one notable exception, vitamin , which the body is able to retain), and so they must be replenished through the diet on a regular, ongoing basis rather than occasionally.
A Few Illustrative Vitamin–Source–Deficiency Links
The precise dietary sources and deficiency diseases for each individual vitamin are catalogued in Table 10.3 below; a handful of examples are enough to show how tightly a single vitamin, a dietary source, and a named disease are linked:
- Vitamin A, obtained from sources such as fish liver oil and carrots, is linked to night blindness when deficient.
- Vitamin (thiamine), sourced from foods like yeast and cereals, is associated with beri-beri on deficiency.
- Vitamin C (ascorbic acid), abundant in citrus fruits, prevents scurvy — its deficiency disease.
- Vitamin D, obtained mainly through exposure to sunlight as well as from fish and egg yolk, guards against rickets in children.
- Vitamin K, present in green leafy vegetables, is required to keep blood-clotting time normal; its deficiency increases the time blood takes to clot.
These are only representative examples — the full set of vitamins, their sources, and the diseases their deficiency produces is considerably longer.
| Sl. No. | Name of Vitamins | Sources | Deficiency diseases |
|---|---|---|---|
| 1. | Vitamin A | Fish liver oil, carrots, butter and milk | Xerophthalmia (hardening of cornea of eye); Night blindness |
| 2. | Vitamin (Thiamine) | Yeast, milk, green vegetables and cereals | Beri beri (loss of appetite, retarded growth) |
| 3. | Vitamin (Riboflavin) | Milk, eggwhite, liver, kidney | Cheilosis (fissuring at corners of mouth and lips), digestive disorders and burning sensation of the skin. |
| 4. | Vitamin (Pyridoxine) | Yeast, milk, egg yolk, cereals and grams | Convulsions |
| 5. | Vitamin | Meat, fish, egg and curd | Pernicious anaemia (RBC deficient in haemoglobin) |
| 6. | Vitamin C (Ascorbic acid) | Citrus fruits, amla and green leafy vegetables | Scurvy (bleeding gums) |
| 7. | Vitamin D | Exposure to sunlight, fish and egg yolk | Rickets (bone deformities in children) and osteomalacia (soft bones and joint pain in adults) |
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